1. Field of the Invention
The invention relates to a flame retardant resin coating comprising a flame retardant base resin and a transparent resin top layer.
2. Description of the Related Art
The use of melamine phosphate and condensed melamine phosphates, such as dimelamine pyrophosphates, to render plastics flame retardant is known in the art. U.S. Pat. No. 4,010,137 describes the use of such flame retardants in polyolefins, and U.S. Pat. No. 3,915,777 describes their use in coatings.
As shown in Chemical Abstracts, Vol. 89: 111478, it is known that melamine phosphate, converted into dimelamine pyrophosphate by the elimination of water, is used as a flame retardant in polyamide that has been filled with a calcium silicate. It has been found that when melamine phosphate and condensed melamine phosphates, such as dimelamine pyrophosphate, are used in polyamides absent fiber reinforcement the results with regard to flame retardancy are unsatisfactory since the desired fire classes are not attained.
WO 96/09344 discloses a flame retardant, glass fiber reinforced polyamide resin compound which comprises from 10 to 40% by weight melamine phosphate, melamine pyrophosphate, particularly dimelamine pyrophosphate or melamine polyphosphate, and mixtures thereof. Further preferred nonhalogen flame retardants which may be present in the polyamide resin compound include zinc borate, zinc phosphate, melamine sulfate or ammonium polyphosphate. Additionally, customary additives, such as lubricants, dispersants, and adhesion promoters may be added, such as stearates, phosphonates, fatty acid amides or Aerosils. Glass fiber reinforced polyamide resin compounds of this type are especially suitable for producing moldings used in the electrical or electronics industry.
WO 99/45061 describes composite materials comprising a fiber material and/or woven material which is impregnated with a resin matrix and cured. The resin matrix, based on a reactive epoxy/anhydride resin, is flame retarded with reactively incorporated phosphorus compounds based on acid derivatives. The flame retardant composite material further comprises fillers, defoamers, leveling assistants, adhesion promoters, and reaction accelerants which are customary in epoxy resin chemistry, such as tertiary amine and/or imidazole or organometallic complexes, for example. The phosphorus content, based on the resin matrix, is from 0.5 to 5% by weight. Composite materials of this kind are used as lightweight materials in vehicle construction, for example, for rail vehicles, bodies of motor vehicles, and marine and aircraft components.
For masking and encapsulating electronic components, WO 94/10223 discloses storage stable and readily curable one component reactive resin systems comprising a mixture of commercially used epoxy resins and phosphorus-containing glycidyl esters, especially diglycidyl phosphonate, and cationic photoinitiators. These reactive resin systems are not curable by means of heat alone, and may be prepared at high temperatures of up to 150xc2x0 C. Even after the reactive resin system has been activated with UV radiation, it remains liquid at room temperature for several months, thereby permitting undisrupted operation. The activated reactive resin system is heat curable at temperatures from 100xc2x0 C. to 150xc2x0 C. In the course of curing, the reactive phosphorus component is incorporated into the reactive resin molding, from which it does not migrate even when said molding undergoes temperature exposure. The properties of flame retardancy conferred by the phosphorus additive on the reactive resin molding are therefore retained. A result of the phosphorus compounds present in the reactive resin system is that the system, which cannot be cured without photoinitiator, is cured rapidly and completely with the photoinitiator, and does not require an additional accelerant.
WO 96/07678 discloses a UV curable one component reactive resin comprising a phosphorus-containing acrylate, a further unsaturated compound capable of free-radical copolymerization with acrylates, and a free-radical photoinitiator system. The phosphorus-containing acrylates may be mixed with a very wide variety of commercially customary acrylate components to give storage stable reactive resins which are suitable for masking electronic components and which, by UV irradiation, cure fully into flame retardant masking compounds. The phosphorus-containing acrylate is obtained as a product of a variety of reactions. For example, a hydroxyalkyl phosphorus compound may be reacted with an isocyanatoalkyl (meth)acrylate or with a methacrylic acid isocyanate. It is likewise possible to react a dihydroxyalkyl phosphorus compound with an active (meth)acrylic acid derivative, or an epoxy phosphorus compound with a hydroxyalkyl (meth)acrylate.
It would be desirable to provide a flame retardant colored resin coating suitable for application to articles exposed to outdoor weathering or to humid, thermal and/or chemical conditions, which colored resin coating remains substantially free from color changes. The present invention provides a solution to this problem.
The present invention provides a flame retardant resin coating comprising a flame retardant base resin and a transparent resin top layer, wherein the base resin comprises color pigments and from about 2.5 to about 50% by weight, based on the weight of the base resin, of flame retardant additives selected from the group consisting of melamine polyphosphates, melamine pyrophosphates, ammonium polyphosphates, and mixtures thereof; and wherein the transparent resin comprises from about 0.5 to about 2% by weight, based on the weight of the transparent resin, of at least one sterically hindered amine.